True, although in very small numbers - AAIB seems to get most of it's expertise from outside as and when required. It has accident-data recorder specialists, technicians and admin support, but those are in small numbers and (bar presumably the administrators) are similarly very experienced people from elsewhere in the industry.
I qualify this by saying that I've never worked for AAIB. I have however helped them out on some half dozen occasions, so think that I have a reasonable feel for what happens there.
G